Self-support phenomenon and formation characteristics of dual synthetic jet

Abstract

A formation criterion of dual synthetic jet (DSJ) is proposed. A DSJ actuator, featured by two cavities, one oscillatory diaphragm, and two exits is a real zero-net mass-flux actuator and has the superiority of higher energy utilization efficiency. However, self-support phenomenon which is unique to DSJ may result in weak jets or even no jets. Two-dimensional numerical simulations have been conducted to investigate the formation characteristics of DSJ. Based on analysis of transverse motion, a dimensionless parameter Stk is drawn out as well as the jet formation criterion of π4a/s<Stk<K. Stk essentially characterizes the unsteady flow both in single cavity and in near field. By analyzing the trend of normalized stroke distance against Stk, DSJ can be classified into four stages for the covered range of simulations. When Stk is lower than 50, jet can’t form. When Stk is in the range of 50<Stk<115, jet can be obtained easily and large stroke distance becomes possible. However, when Stk increases up to the range of 115<Stk<420, self-support phenomenon occurs and jet becomes weak. In this stage, an inflection point locates at about Stk=310. No jet but a circumfluence region is available when Stk>420. A different velocity boundary condition also has been tested and the results conform to the proposed jet formation criterion too. The formation criterion and characteristics can serve as a useful design guide for DSJ.